Conventional turbine engine auxiliary power units are well known in the aerospace technologies. These units are used to provide power to the aircraft either on the ground or in flight, or both. This power may be provided in the form of one or more of electrical power, hydraulic power, pressurized air, or another form, according to the requirements of the aircraft in which the APU is installed. Unfortunately, starting of an APU may require from many seconds to as much as a few minutes. During this starting time power from the APU is, of course, not available to the aircraft. As a result, some essential aircraft systems may not be operated during starting of the APU. Also, if the aircraft is above a determined altitude, it is not possible to start the APU because of low ambient pressure. An aircraft with only an APU may require some other system, such as an EPU or a ram air turbine, to provide power to the aircraft until the APU can be started.
Similarly, EPU's are known which employ a hydrazine decomposition chamber, for example, or a jet fuel combustor to provide a flow of high temperature pressurized motive gas to a turbine. The turbine is employed to drive a hydraulic pump or electric generator, for example. The EPU is employed to provide hydraulic or electric power (or both) on a relatively short term basis after a failure of an essential system associated with the aircraft main engines. This emergency power supply allows continuation of controlled aircraft flight for a limited time while the aircraft is brought to a landing or to an altitude low enough to allow starting of the aircraft APU.
The development of unstable aircraft has in particular increased the necessity for providing a rapidly available source of emergency power. Upon a failure of the main hydraulic pump, or main generator, or of the aircraft propulsion engine driving these devices, the aircraft cannot be maintained in controlled flight. Without hydraulic power to move aircraft control surfaces, or electrical power for flight control computers, the unstable aircraft is uncontrollable. Thus, these aircraft must have a source of emergency power which is available almost immediately after the failure of a flight control related power system. Unfortunately, the conventional technology for this purpose employs hydrazine fuel and a decomposition chamber containing a catalytic reaction bed. When such an EPU is operated, even for a short time, the toxic hydrazine must be flushed from the aircraft system using neutralizing chemicals, and the decomposition chamber must be replaced.
As a result, a transient in the aircraft systems, for example, which does not represent a genuine emergency, but which exercises the EPU can be very expensive. Also, this type of unnecessary exercise of the EPU may compromise the availability of the EPU for operation were a genuine emergency to occur. As a result, EPU's which employ hydrazine and a decomposition chamber are widely recognized as an unsatisfactory solution to the need for an emergency power supply aboard aircraft.
Additional shortcomings of conventional technology which provides both an APU and a separate EPU are that the weight, size, fuel consumption, complexity, cost and maintenance requirements of the aircraft are all increased while the performance of the aircraft is decreased.
In view of the recognized deficiencies of conventional technology in the aircraft APU and EPU fields, it is an object for this invention to provide a multifunction integrated power unit (MIPU) which performs the functions of an APU and an EPU, while being smaller and lighter in weight than the total of the two conventional units which it replaces.
An additional object is to provide a MIPU of the above-described character which does not require hydrazine or other similar toxic or unstable chemical for its operation.
Still another object for the present invention is to provide a MIPU having both APU and EPU functions while using only a single fuel.
Yet another object for the present invention is to provide a MIPU combining functions of an EPU and an APU and which can transition from one function to the other with no interruption in power supply to the aircraft.
Still another objective for the present invention is to provide a selective clutch device which delivers power from one of the APU or EPU to the power consuming accessory devices, and which may be conveniently removed from the MIPU and serviced or replaced without extensive disassembly of the MIPU.
Accordingly, the present invention provides a power transfer unit comprising an elongate tubular member, said tubular member externally defining first cooperating means for journaling said tubular member upon a housing, said tubular member externally defining second cooperating means for rotatable shaft power distribution delivering torque from said tubular member to a shaft power consuming device, and a pair of oppositely disposed one-way overrunning clutches carried within said tubular member, each of said pair of clutches being disposed to transmit torque to said tubular member in one rotational direction and to allow said tubular member to overrun relative thereto in said one direction, when said tubular member is rotationally driven at a higher speed by the other of said pair of clutches, each one of said pair of clutches including means for receiving shaft power transmitted thereto.
An advantage of the present invention is that the MIPU may operate on the same jet fuel used in the propulsion engine of the aircraft to provide both EPU and APU functions.
Additional advantages provided by the MIPU of the present invention is the reduction in size, weight, cost, complexity, and maintenance requirements made possible in the aircraft itself resulting from the use of the MIPU rather than separate EPU and APU units.
Still further, the MIPU may be serviced to repair or replace the selective clutch which selects shaft power from one or the other of the APU or EPU portion of the MIPU without extensive disassembly thereof.
Additional objects and advantages of the present invention will appear from a reading of the following detailed description of a single preferred embodiment of the invention taken in conjunction with the appended drawing figures, in which: